A transmission is any mechanical linkage that converts an input torque to an output torque. It usually involves a series of gears that have differing diameters, allowing a first gear at a first rotation rate to link to a second gear rotating at a second rate. The most common application for transmissions is in a vehicle. For example, a car may have an automatic transmission or a manual transmission. A bicycle has a simple transmission that links the pedals to the hub of the rear wheel.
Transmissions allow an input force to be converted into a more useful and appropriate output. However, by using gears and linkages, a typical transmission may only have 4 or 5 ratios available. For example, a four speed automatic transmission in a car has only 4 sets of output gears to couple to the engine's input. A ten speed bike has only ten ratios of input to output. A need exists for a transmission that is not limited by the number of gears. Yet, to place a larger number of gears into a transmission increases its costs and weight and space requirements.
A continuously variable transmission (CVT) is a transmission that eliminates the need for a specified number of gears. Instead it allows an almost limitless number of input to output ratios. This is a benefit because it allows an output to be achieved (i.e. the speed of a vehicle) at an optimal input (i.e. the rpm of the engine). For example, an engine might be most efficient at 1800 rpm. In other words, the peak torque output for the engine might be achieved at this engine rpm, or perhaps the highest fuel economy. Consequently, it may be desirable to run at a specified RPM for an economy mode or a power mode. Yet, in third gear, the car might be going faster at 1800 ipm than the driver desires. A continuously variable transmission would allow an intermediate ratio to be achieved that allowed the optimal input to achieve the desired output.
CVT transmissions have a variator for continuously variable adjustment of the ratio. A customary structure is a belt drive variator having two pairs of beveled pulleys and rotating a torque-transmitter element therein, such as a pushing linked band or a chain. The beveled pulleys are loaded with pressure from the transmission oil pump in order, on one hand, to actuate the ratio adjustment and, on the other, to ensure a contact pressure needed for transmission of the torque upon the belt drive element. Another usual structure is a swash plate variator in semi-toroidal or fully toroidal design.
Examples of CVTs are exemplified by U.S. Pat. Nos. 6,419,608 and 7,011,600 assigned to Fallbrook Technologies of San Diego, Calif., the contents of which are hereby incorporated by reference. In each of those applications the axial movement of a rod or an axial force (as indicated by numeral 11 in each reference) is used to vary the input-to-output ratio of such transmissions.
FIG. 1 is a prior art schematic representation depicting the operation of manually controlled CVT or variator in a light electric vehicle, such as a scooter. As shown in FIG. 1, a manual push button control box 101 has buttons corresponding to a signal output 108 of 0% 102, 25% 103, 50% 104, 75% 105, and 100% 106 sent to a microprocessor 112. The microprocessor output can be shown on a display 150. The microprocessor 112 interfaces with a motor control board 114 which receives power from a battery pack 118.
A servo motor 120 engages a 90-degree gearbox 122 which provides an axial force 130 to a variator (CVT) 132 in contact with the rear wheel 134. The rear wheel 134 is powered by a chain 136 or other equivalent means connected to a drive motor 140 (e.g., Briggs & Stratton ETEK).
The speed of the drive motor 140 is regulated by a current sent by a motor control device 144. The motor control device 144 is regulated by a throttle 146 and is powered by the battery 118.
While a user of the electric vehicle can manually shift gears using the push button control, it would be desirable to have an automatic shifting transmission to permit an electric scooter to operate in a power mode or an economy mode. Consequently, a need exists to automatically adjust the input to output ratio based upon one or more input variables.